Interlocking Well Isolation Layout for CMOS Latch-Up Prevention
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Solution Overview
Problem
Conventional latch-up prevention structures in CMOS ICs, such as guard rings and tap cells, occupy significant real estate on IC chips and are not entirely satisfactory in preventing latch-up due to the need for isolation structures that displace functional devices and introduce layout-dependent effects.
Innovation Solution
The use of fin-cut dielectric features formed after source/drain and metal gate structures to isolate tap cells from standard cells, eliminating the need for OD breaks and allowing for smaller isolation structures, and interlocking well shapes to minimize area usage and improve performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional isolation structures are used to isolate tap cells from standard cells, then latch-up prevention is achieved, but the area occupied by isolation structures increases, displacing functional devices
Solution Approach 1:
The isolation structure is segmented into multiple portions: a first isolation structure portion and a second isolation structure portion. The first portion has a first cross-sectional area and the second portion has a second cross-sectional area that is smaller than the first. This segmentation allows the isolation structure to provide adequate latch-up prevention while reducing the overall area occupied, particularly at the boundaries where isolation is most critical.
Solution Approach 2:
The isolation structure employs varying cross-sectional areas at different locations. The first isolation structure portion has a larger cross-sectional area where it is most needed for latch-up prevention, while the second isolation structure portion has a smaller cross-sectional area where less isolation is required. This local quality variation optimizes the balance between reliability and area efficiency.
2Reliability
If tap cells are isolated from standard cells using conventional methods, then latch-up prevention is maintained, but layout-dependent effects are introduced
Solution Approach 1:
The isolation structure transitions from a static, uniform design to a dynamic, variable design where the cross-sectional area changes along the length of the isolation structure. This dynamic variation allows the isolation effectiveness to be optimized at different locations while minimizing the introduction of layout-dependent effects, as the structure adapts to the local electrical environment.
3Reliability
If larger isolation structures are used to ensure adequate latch-up prevention, then reliability is improved, but the available space for functional devices decreases
Solution Approach 1:
By segmenting the isolation structure into portions with different cross-sectional areas, the design provides adequate latch-up prevention in critical regions while minimizing the area consumed in regions where less isolation is needed. This segmentation strategy directly improves functional device density by reducing the total area occupied by isolation structures.
Solution Approach 2:
The cross-sectional area parameter of the isolation structure is varied along its length, with the first portion having a first cross-sectional area and the second portion having a second cross-sectional area that is smaller. This parameter change optimizes the balance between latch-up prevention effectiveness and area efficiency, thereby increasing the space available for functional devices.
Data Source
AI summary
A semiconductor structure includes a first well doped with a first dopant and a second well doped with a second dopant different from the first dopant. From a top view, the first well includes a first base extending lengthwise along a direction, and a first letter-shaped portion and a second letter-shaped portion connected to the first base. From the top view, the second well includes a second base extending lengthwise along the direction and a third letter-shaped portion connected to the second base. The third letter-shaped portion extends into the first well and is keyed to the first letter-shaped portion and the second letter-shaped portion.